M- _P._Vol. I.] DAVIDSON— APPARENT PROJECTION, ETC. 79 



conditions, with the Lick thirty-six-inch objective, " the limb 

 of Jupiter has appeared perfectly opaque, as in all my previous 

 observations with smaller telescopes." But he makes no 

 reference to the character of the factitious limb of the 

 planet in unfavorable conditions of the atmosphere. 



At Melbourne, September 14. 1879, the occultation of 64 

 Aquarii (6.9 magn.) by Jupiter was watched in the great 

 reflector. The star was thirty-five seconds in disappearing, 

 and remained visible ten seconds longer as a speck of light 

 seen through ground glass. This speck " also disappeared 

 gradually." Proctor says the observers personally assured 

 him the phenomenon was not due to irradiation. 



In 1878, at the Adelaide Observatory, two observers 

 (Messrs. Todd and Ringwood) saw the occultations of 

 satellites I, II and III upon certain occasions "within the 

 disc of the planet " at disappearance, and once at reappear- 

 ance. " In every other case the occultation was perfect at 

 the limb." This latter sentence was not quoted by Proctor. 



Dr. E. C. Pickering, Director of Harvard Observatory, 

 has described an occultation of D.M., 23° 1087 (7.3 magn.), 

 by Jupiter, April 14, 1883. He used the fifteen-inch 

 objective, with achromatic eye-piece, power 400. " For a 

 period of about ten minutes after disappearance was 

 observed, the star is recorded as 'suspected.' The record 

 states that for some time previous to final disappearance 

 ' the star alternately disappeared and reappeared without 

 cause; seeing pretty good and uniform throughout.' At 

 the reappearance, the limb of the planet was watched con- 

 tinuously for forty-nine seconds, at the beginning of which 

 the star was not visible, and at the end of which it was dis- 

 tinctly seen, remaining visible thereafter." 



In our experience in observing Jupiter, we have never 

 seen the border sharply defined when using powers of 500, 

 but atmospheric conditions have never been supremely 

 good at the times of observation. In observing the occul- 

 tation of Jupiter's satellites through an unsteady atmosphere, 

 our fellow-observer, with a smaller telescope and objective 



( 2 ) November 19, 1900. 



